1. Field Of The Invention
The present invention relates to those refrigeration systems that are especially suitable for use in refrigerating food products displayed in refrigerated display cases, especially though not necessarily those of the open front type, installed in food supermarkets. In a more particular sense the invention may be classified as an improvement in refrigeration systems of the type that utilize the concept of effecting power savings through sub-cooling of a refrigerant within a condenser exposed to outside ambient air temperatures. In systems of this type, natural sub-cooling is controlled in a manner to reduce compressor operation with resultant power savings. This is done by varying the effective capacity of the condenser through controlled flooding thereof.
In yet a more particular sense the improvement comprising the present invention can be appropriately classified as an automatic control in refrigeration systems of the category described in which pressures within a surge receiver are automatically regulated to closely follow an automatic condensing and compressor discharge pressure regulating function.
2. Description Of The Prior Art
A refrigeration system in which the present improvement is especially suited for use is exemplified by U.S. Pat. Nos.3,905,202 to Taft et al; and 4,012,921 to Willitts et al.
A system of the type disclosed by these patents works admirably, in effecting power savings under a wide variety of differing outside ambient air temperatures. However, under certain circumstances it becomes desirable to incorporate additional, improved features in such systems, as regards establishing and maintaining pressures in the surge receiver characteristically employed in such a system.
At present, there is provided, in the patented systems referred to, means in the form of an outlet pressure regulating valve, connected between the compressor discharge and the receiver. This valve has been sensitive to existing receiver pressures. The valve has a fixed setting, and whenever the receiver pressure drops below this setting, the valve opens to communicate the compressor discharge with the receiver, to raise the receiver pressure to the fixed setting.
Keeping in mind that the receiver pressure must at all times be lower than the head pressure of the system (that is to say, the pressure in the discharge line extending from the compressor to the condenser), a problem has been produced in that one cannot operate the system at head pressures lower than the fixed receiver pressure control valve setting. This has reduced the versatility of the system and the capability thereof as regards saving energy.
A problem of at least equal or perhaps even greater significance, in the prior art, results from the fact that utilizing a fixed setting in the receiver pressure control valve arrangement, sensitive only to existing receiver pressure, has produced "logging" of liquid within the receiver, under certain circumstances. This is a condition in which the receiver tends to fill with an excessive amount of liquid, and as a consequence tends to deprive or "starve" the expansion valves associated with the several evaporators. Starving of the expansion valves means that the valves are not supplied with sufficient liquid condensate to efficiently discharge their function.
For the reasons given above, the prior art devices have failed to operate with as much efficiency, in all types of outside ambient air temperature conditions, as would be desirable. This undesirable condition, it is believed, derives from an inherent lack of flexibility in the means for controlling receiver pressures. This lack of flexibility in respect to the control of receiver pressures has in turn produced a corresponding, undesirable limitation of the range of condensing and head pressures considered desirable to make optimum usage of the widely varying ambient temperatures found in the various seasons of the year. Thus, while atmospherically responsive refrigerating systems of the type disclosed in the above-mentioned patents represent an important advance in the art, it has been found desirable to increase the general capability thereof for making the most efficient use possible of varying climatic conditions.